1. Field of the Invention
This invention relates to the field of data processing systems. More particularly, this invention relates to the detection of malicious computer program activity, such as, for example, as the result of computer viruses, worms, Trojans and the like, using detected characteristics of external program calls.
2. Description of the Prior Art
It is known to provide anti-virus systems which examine computer files to be accessed to determine characteristics of those computer files known to be indicative of malware, such as computer viruses, worms, Trojans and the like. Such techniques are necessarily reactive in that a new piece of malware must first be released and identified before the characteristics of that new piece of malware can be determined such that the detection mechanisms can be updated to detect that new piece of malware. An alternative type of anti-virus system uses heuristic methods in which the computer file is examined to identify types of activity it is controlling and, if these match known suspicious types of activity, then an anti-malware response may be triggered. Whilst such an approach can provide some protection against newly released malware, it does suffer from requiring a disadvantageously high processing overhead.
It is also known to provide anti-virus systems which examine the behaviour of a computer system at the level of external program calls being made to the operating system. It has been found that certain sequences of external program calls, or combinations of external program calls with certain characteristics, are indicative of malicious computer program activity and may be used to trigger anti-malware responses. A problem with this behavioural analysis approach is that the malicious activity against which a defense is being sought is allowed to occur prior to it being detected. Accordingly, some damage may already have been inflicted upon the computer system concerned by the malicious computer program activity, e.g. the malicious computer program may already have managed to replicate itself and infect further machines.